Fix minimum PHP version

README.md

@@ -4,7 +4,7 @@ STOMP protocol implementation
 [![Build Status on TravisCI](https://secure.travis-ci.org/xp-forge/stomp.svg)](http://travis-ci.org/xp-forge/stomp)
 [![XP Framework Module](https://raw.githubusercontent.com/xp-framework/web/master/static/xp-framework-badge.png)](https://github.com/xp-framework/core)
 [![BSD Licence](https://raw.githubusercontent.com/xp-framework/web/master/static/licence-bsd.png)](https://github.com/xp-framework/core/blob/master/LICENCE.md)
-[![Required PHP 5.5+](https://raw.githubusercontent.com/xp-framework/web/master/static/php-5_5plus.png)](http://php.net/)
+[![Required PHP 5.6+](https://raw.githubusercontent.com/xp-framework/web/master/static/php-5_6plus.png)](http://php.net/)
 [![Supports PHP 7.0+](https://raw.githubusercontent.com/xp-framework/web/master/static/php-7_0plus.png)](http://php.net/)
 [![Latest Stable Version](https://poser.pugx.org/xp-forge/stomp/version.png)](https://packagist.org/packages/xp-forge/stomp)